Temperature indicator



Jan. 9, 1945. v

F. 13. SIAS TEMPERATURE INDICATOR 2 Sheets-Sheet 1 Original Filed Nov.9, 1942 Frederick R. SiaS,

His Zttor-ney.

Jan. 9, 1945. F. R. slAs 2,367,065

I TEMPERATURE INDICATOR Original Filed Nov. 9, 1942 2 Sheets-Sheet 2Inventor: Fredefick R. Sias,

His Attorney.

Jan. 9, 1945 Frederick R. Sias, rein-bi to General Electric-Company,

New York ehead, Mass, assignor a orp ration of Original applicationlilovember 9, 1942, Serial No. 465,079. Divided and this applicationJune 10,

1943, Serial No. 490,347-

. i Claims .1 (01. 171-195) This application is a division of myapplication BeriaINo. 465,079, filed November 9, 1942, and reiatesprimarily to an improved measuring circuit for an indicating systemprovided with ambient temperature compensation and scale angle ad-Justment. Another divisional application Serial No. 521,255, filedFebruary 5, 1944, relates to the double bridge circuit described herein.

Other and further objects will become apparen as the descriptionproceeds.

In carrying out my invention in its preferred form for the measurementof temperature I utilize a Wheatstone bridge circuit having constantresistance arms and an arm which varies in resistance in accordance withvariations in temperature, and I employ a two-circuit current responsiveinstrument having one winding connected at the diagonal arm or bridgebalance responsive element and having another winding so connected as toprovide a controlling torque.

' In the form of my invention which I now conposition within the deviceas illustrated in Fig. 1;

sider the preferred form the current responsive instrument comprises across coil instrument having the main winding mechanically divided intoseveral parts, and having an auxiliary windingmechanically divided, intotwo parts mounted with a magnetic axis at right angles to the magneticaxis of the main winding, having fewer turns and having less pole widththan the main winding so as to provide a narrow magnetic field incomparison with the main winding. To co- W operate with the electricalwindings, I provide a permanent magnet rotor of high coercive forcelight weight magnetic material having the shape of a flattened rightcircular cylinder magnetized transversely to its axis in a directionparallel to the flattened sides. The apparatus is so arranged that therotor is in its'mid scale position when the magnet is in alignment withthe magnetic axis of the auxiliary winding so as to give the auxiliarywinding the greatest eiIect upon the rotor when it is in the mid scaleposition.

- A better understanding of myinvention will be aflorded' by thefollowing detaileddescription considered in connection withtheaccompanying drawings. and those features or the invention which arebelieved to be novel and patentable will be pointed out in the claimsappended hereto. t I

In'the drawings Fig. 1 is aperspective viewof a cross-coilcurrent-responsive instrument formm 'one embodiment of myinvention; F18.2 is a view showing a section cut by plane 2-! passing through therotoraxis of the apparatus of 1; Fig. 3 is a perspective view, slightlyensrsed. of Fig.

of the inner mechanism of the apparatus 1 shown as turned 90 degreesfromits Fig. 4 is an exploded perspective view of the mechanism of Fig3.with the rotor shaft and pointer shown in addition; Fig. 5 is aschematic electric circuit diagram for one embodiment of my inventionfor measuring temperature; Fig. 5A is a schematic diagram explaining theprinciple of operation'of the apparatus of Fig. 5; Fig. 5B is afragmentary diagram of a modification in the arrangement of Fig. 5; Fig.6 is a circuit diagram of a modification in the arrangement of Fig. 5utilizing asimplified circuit; Fig. 7 is a schematic circuit diagramillustrating a circuit for a resistance type temperature measuringsystem which is especially well adapted for an-in strument or the typeillustrated in Figs. 1 to 4; Fig, 8 is a vector diagram explanatory ofthe principle of operation of the apparatus of Fig. 7 and the manner inwhich temperature compensationis obtained; .and Fig. 9 is a vectordiagram explanatory of, the principle of operation of the instrumentillustrated in Figs. 1 to 4 and showing the manner in which linear scalecalibration is obtained. Like reference characters are used throughoutthe drawings to designate like parts. Wheatstone bridge. circuits may beutilized for the measurement of. temperature if one of the arms .of thebridge is composed of resistance material withanappreciable temperaturecoefllcient of resistance in comparison with other arms of the'bridge. Asingle coil instrument, such as a galvanometer or a milliammeter, may beconnected in the. diagonal arm of the bridge and variationsin'temperature will cause variations in the condition of balance orextent of unbalance of the bridge so as vto produce variations incurrent and, consequently; deflection of the instrument in response tovariations in temperature.

The effect of variations involtage oi the cur rent source for,energizing the bridge may be overcome or minimized by using a ratio typeof instrument or; cross-coil instrument having a main winding responsiveto the condition of balance of the'brid'ge and an auxiliary windingconnectedto the current source. I have found that is employed havingoperating coils connected with magnetic axes substantially at rightangles. The coils or windings oi the instruments are connected in thecross arms of the respective bridge circuits.

As illustrated in Fig. one o! the bridge circuits consists of resistorsll, l2, "and I4 connected in series parallel to a source oi energizationcurrent such as a battery it with input terminals l8 and il serving asthe energizing terminals of the bridge and terminals II and I! servingas the conjugate terminals of the bridge across which the diagonal armmay be connected. The diagonal arm consists of a coil A which forms oneor the windings of a cross coil current responsive instrument. Thesecond bridge has two arms in common with the first bridge andcomprises, in addition to the resistors i2 and I4, a second pair 01'resistors 20 and 2! connected in series between the energizing terminalsII and II which are common to the flrst bridge and are connected to thebattery It. The conjugate terminals oi the second bridge consist of theterminal l9 and the Junction terminal 22 of resistors 20 and 2|, and thediagonal arm oi the second bridge consists of a coil B which forms thesecond winding of the cross-coil instrument.

Two of the resistors forming symmetrically arranged arms of the doublebridge circuit, for example, the resistors l3 and 2i, are composed of amaterial the resistance of which varies appreciably with temperature'incomparison with the temperature effect of the other resistors.Preferably, in order to accentuate the effect, the other resistors arecomposed of a material which has little or no temperature coefllcient o1resistance such as maganin or constantin, for example, or some othersuitable material well known to those skilled in the art. The resistorsi3 and 2| may be composed of copper or nickel wire or any other suitablematerial known to those skilled in the art having a relatively hightemperature coefllcient of resistance.

For the type of operation desired under ordinary circumstances, it ispreferable to select the dimensions of the electric circuit elements ofthe resistance bridge arms so that the bridge circuits will be balancedat two diiierent temperatures within the desired range of temperatureindication. For normal conditions the preferred arrangement is to haveone of the bridge circuits balance at a temperature representing Vs thedesired total scale angle and the other bridge circuit balanced at atemperature representing 9g of the desired total scale angle.

Let it be assumed, for instance, that the bridge consisting of theelements A, ll, l2, l3 and I4 is balanced at a temperature As the way upscale from the minimum temperature to be measured by the apparatus. Whenthis temperature exists no current will flow in the coil A and thedirection of the magnetic flux will be determined wholly by the positionof the coil B. The crosscoil instrument comprising the coils A and B isrepresented schematically in Fig. 5A where the coils A and B are shownmounted at right angles to one another with magnetic axes intersectingand with a transversely magnetized rotor 23 mounted with the axis ofrotation passing through the intersection of the magnetic axes of thecoils A and B and perpendicular thereto. If desired, the windings A andB may each be divided into two coils connected in series and mounted onopposite sides of the rotor 23. The current responsive instrument may beof the type illustrated in Patent No. 2.24am ted to Faus, but with fourcoils and with the opposite coils connected in series and in separatecircuits to term the windings A andB.

As the temperature deviates above or below the value at which zerocurrent flows in the coil A, the bridge including the coil A will beunbalanced in one directionor the other, and current will flow throushthe coil A in one direction or the other producing deflection oi therotor 28 according to the direction 0! deviation of the temper ture. Atthe assumed temperature it of the way up the scale, when the amount ofcurrent flowing in the coil A is zero and the position oi. the rotor 23is determined entirely by the coil B, the magnetic rotor 23 will take upa position with its poles NS along the magnetic axis of the coil Brepresented by the arrow 24 as illustrated in Fig. 5A. When thtemperature falls to a um, current will flow in the coil A and the fluxis assumed to be in such a position as to deflect the rotor 23 totheleft to the position represented by the arrow 25. Since the coil B isalso carrying current the arrow 25 will be at some position representingthe resultant oi the fluxes of the coils.A and B. As the temperaturerises to mid scale the rotor 23 will deflect in the other directiontoward a resultant position represented by the arrow 26 half way betweenthe coils A and B. At a temperature represented by the a. position onthe scale the rotor will take the position of the arrow 21 through themagnetic axis of the coil A, since then the bridge i2, ll, 20, H isbalanced and no current flows through the coil B.

At the maximum temperature the rotor will take up a position representedby the arrow 28 beyond the coil A. The angular distance between themaximum and minimum points 25 and 2t wili approach degrees.

It will be observed that the currents in the coils A and B each reverseas well as vary in magnitude in accordance with variations intemperature, thus bringing about the long scale angle of the system.

Although the arrangement of Fig. 5 is particularly well adapted for themeasurement of tem-- perature it is not limited thereto and may be usedalso for the measurement of resistance, for example, or to form a remoteposition indicator. For example, the resistors 13 and 2! may be re-Dlaced by a telemeter transmitter resistor 29, shown in Fig. 5B, havinga mid terminal ll dividing the resistor into two parts, i3 and 2 icorresponding to the resistance arms l3 and M. In place of fixedconnections to the ends of the resistor 29 adjustable connections i8 and22' corresponding to the terminals i8 and 22 of Fig. 5 may be used. Theadjustable connections is and 22' serve for scale end adjustment. Inplace of the fixed connection between the resistor M and the junction ofthe bridge arms l3 and H a movable brush 30 is utilized in thearrangement of Fi 5B. The brush I0 is slidable along the resistor 29 inresponse to change in an indication or a position to be remotelyindicated. For example, the brush 30 may be connected by a linkage (notshown) to a float arm attached to a float in a fuel tank in order toform a remote indicating float gauge with a scale angle about 150degrees long.

If a slightly shorter scale angle is suillcient, a simplifiedarrangement of Fig. 6 may be employed which utilizes only a singlebridge and only one bridge arm, the resistance of which varies withtemperature. With this arrangement a scale length of about 120 degreesmay be obtained. Any one of the bridge arms may be composed of aresistance material which varies in resistance with temperature. As inFig. one of the instrument coils A is connected across the conjugatedterminals of the .bridge l8 and IS. The second coil of the instrument,however, in this case designated B', is utilized as an auxiliary windingand is connected in series with a resistor 31 across one of the arms ofthe bridge, for example, the bridge arm designated l4". The bridge arml3" may have a resistance varying with temperature as in the case ofFig. 5. However, a slightly greater deflection may be obtained by makingthe arm I4" or the arm II the temperature variable resistance arm so asto produce variations in current flow in the coil B as well as in thecoil A in response to variations in temperature. It will be understoodthat if the coil were shunted across a resistor included in a constantresistance circuit, it would act merely as a biasing coil and thecurrent therein would not vary in response to variations in temperature.

It will be understood that the arrangements of Figs. 5and 6 may also beutilized with a battery having one terminal grounded in order tominimize the number of insulated conductors required. For example, ifone of the terminals of the battery 15 is connected to a groundconnection 32, the lower ends of the resistors l3, l4, 2|, l3", l4" and3| may be grounded at the most convenient locations instead of beingconnected by means of insulated conductors to the terminal H.

The arrangement of Fig. 6 is preferably so adjusted that the bridge isbalanced at the center scale position of the instrument and theresistance of the resistor 3| is so chosen that the pointer deflects tothe ends of the scale at the temperatures which are to be the maximumand minimum temperatures of the range for which the temperaturemeasuring system is to be used.

In the arrangement 01 Fig. '7, in order to have a highly compactsensitive arrangement, I employ a main winding A wound from many turnsof wire and I employ an auxiliary or control winding B which consists ofiewer turns and I connect the winding 13 in series with the currentsource l5 to the bridge I I, l2, l3 and H. In this manner ample currentis available for energizing the winding B, since the winding B carriesthe full bridge current except for that carried by a resistor 33connected in shunt to the winding B for temperature compensation. Theresistor 33 may be made adjustable if desired for the purpose ofadjusting scale length, since for a fixed adjustment of the resistor 33the winding B carries a fixed current, whereas the-main winding Acarries a reversible current variable in response to variations intemperature. Under normal condi tions the resistances are so chosen thatthe bridge is balanced at the center scale temperature.

The variable resistance arm [3, a in the case of Figs. 5 and 6, may becomposed of any suitable resistance materialhaving an adequatetemperature coefficient 01 resistance. It may, for example, consist ofthermometer resistance wire wound on an insulated form and enclosed in aprotective shell from which it is insulated to form a so-calledresistance bulb of the type described in Patent No. 2,149,448, grantedto Lederer.

In order to protect the parts of the apparatus in the event 0! apossible short circuit, I prefer to connect a resistor 34 inseries withthe current the scale is R2.

source II, the resistance of the resistor 34 bein determined by thevoltage of the source IS.

The manner in which the circuit of Fig. 7 serves to provide indicationsof temperature and give a wide angle or deflection of the currentresponsive instrument is shownin Fig. 8. The flux of the winding B whichremains substantially constant is represented by the vertical vector andthe flux of the coil A at right angles thereto at a given maximumtemperature T1 is represented by the vector T1. The rotor of thecurrentresponsive instrument takes up an angular position determined bythe resultant of the vectors A and B, viz: the vector R. Thecorresponding resultant vector for the minimum temperature of By makingthe coil A stronger than the coil B it will be observed that a wideangle of deflection is obtained, the angular length of the scale beingrepresented by the angle between the vector R and the dotted vector Ra.In the event the temperature varies from T1 to T2 the resultant fieldproduced by the windings A and B is the resultant of the vectors T2 andB or R. Thus, as the temperature varies the reresultant flux and therotor position varies between the angular positions of R and R2. With afixed amount of variation in the vector flux A. changes in B will affectthe total indicator scale angle. Therefore the scale angle may beadjusted by adjusting the resistance of the shunt 33 to allow forvariations in manufacturin tolerances.

One of the important advantages of the circuit of Fig. 7 is the factthat only the winding A need be highly sensitive as the winding B may beexcited by any reasonable amount of current. However, if desired, thecircuit may be rearranged to have the coil B with its compensating shuntand a series resistor shunted around the bridge in which case adjustmentof the series resistor would form the adjustment of the length of scaleangle. Also the complete bridge may be shunted by an adjustable resistorfor adjusting the current through the coil B to control the scale angle.

The manner in which the circuit of Fig. '7 compensates for variations inambient temperature will be better understood by first considering theoperation in the event that the compensating resistor 33 is omitted. Itwill be assumed that all the resistance other than the resistance of thecoils A and B and the resistance of the bulb l3 are relatively constantand will have negligible temperature coefllcients oi.

resistance. The resistance of the series resistor 34 tends to swamp outvariations in resistance of the coil B and the current flowing throughthe coil B tends to remain constant as the ambient temperature varies.However, the variation in ambient temperature produces variations in theresistance of the coil A which is wound of copper wire and,consequently, a deflection of the instrument varies with variations inambient temperature. On the other hand, when the resistor 33 isconnected, variations in ambient temperature will cause variations inthe diversion of current between the shunt 33 and the auxiliary coilB,because the coil B is wound of copper which varies in resistance withambient temperature, whereas the resistance of the shunt 33 remainsrelatively constant. As the temperature rises, causing the current todiminish in the coil A, more current is diverted from the coil 3 to theshunt 33 and the coil B is accordingly weakened as the current in thecoil A is weakened. Itv

will be understood that the most accurate temperature compensation willbe obtained by proper selection of the ratios between the resistances ofthe elements 13 and 33 at the average ambient temperature. I have foundthat indications may be made accurate to a fraction of a per cent overan ambient temperature range of from 50 degrees below zero to 70 degreesabove zero C.

A'current responsive instrument construction, especially well adaptedfor use with the arrangement of Fig. '7, is illustrated in Figs. 1 to 4.The apparatus here illustrated comprises a suitable insulating base andconnection block 35 supporting a housing or frame 36 composed of amaterial such as cast aluminum, for example, in which are mounted thewindings A and B and a magnetic rotor 31 cooperating with the electricalwindings A and B.

The main winding A is wound on a separable coil form in order that itmay be mounted around the rotor. It may be divided into a plurality ofparts so as to form a winding mechanically divisible into a plurality ofwinding spools, e. g., iour winding spools carrying mechanicallyseparate coils 31', 38, 39 and 40, as shown in Figs. 3 and 4. Thesecoils correspond to winding A, Figs. 5, 5a, 6 and 7. The coils 31 to 40are electrically connected in series, however, by conductors (notshown). For the sake of maximum compactness the coils 31' to 40 are soformed and mounted as to fill as nearly as possible a circumscribing cylinder represented by the inner surface of a mag netic shield 4| composedof suitable high permeability material such as Mu metal, for example.

The coils 38 and 39 are left sufllciently narrow, however, to leavespace at the sides for thin coils 42 and 43 which form two mechanicallyseparate parts of the auxiliary winding B, which are also electricallyconnected in series by conductors (not shown). As shown by the drawingin order to flt a circular contour more closely, the outer coils 31 and40 of the winding A are made narrower than the inner coils 38 and 39.The division of the winding A into four mechanically separate coilsmakes it possible to wind fully each of the four separate winding partsor coils so as to obtain the maximum winding cross-section in each suchpart without danger of inadequate mechanical support or diificulty fromsliding wires encountered in attempting to wind a coil which is taperedin thickness or has substantially diflerent coil thickness in difierentparts of the coil. The separability of the winding A also facilitatesassembly of the apparatus.

The larger inner coils 38 and 39 are wound on separable winding formswhich may be thought of as single-flange spools 44 and 45 comprisingflanges 46 and 41 integral with hollow cores or shells 48 and 49respectively. Each of the shells 48 and 49 is semi-cylindrical in shapeso that when the winding forms 44 and 45 are fitted together acylindrical space is provided within the coils to receive the rotor 31.The shells 48 and 49 may be composed of a suitable conducting materialsuch as copper, so as to form a damping cup. Each has a projection, onlyone of which,

50, is visible, serving to support winding forms or.

spools 5| and 52 carrying the coils 37' and 40, respectively. Each ofthe spools 5| and 52 consists of an inner flat rectangular flange 53 andan outer flange 54 which is a segment of a cylinder with an integralcore 55 having an opening fitting the projection 50 of the inner windingform 44 or 45. countersunk screw holes 58 and threaded holes 5'! areprovided in the outer and inner winding forms respectively to permitassembly of the winding A by means of screws, only one of which, 58, isshown in Fig. 3. The inner flanges 53 of the outer spools 5| and 52serve also as outer flanges of the inner spools 44 and 45.

The parts 42 and 43 of the auxiliary winding B are also wound on coilforms or spools 59 which are shown to be thin and slightly curved inorder to fit within the cylindrical surface of the shield 4| (Fig. 2).The coil forms 59 for the winding B have long rectangular openings6lland it will be observed that the flanges 43 and 41 of the inner coilforms of the winding A have side projections 6|, of suchdimensions as toform a support over which the opening 80 may be fitted when the coil Ahas been assembled as'shown in Fig. 3.

It will be seen that each of the coil forms 59 for the auxiliary windingB serves also to hold together the projection SI of the coil forms ofthe main winding A so as to hold this winding in assembled relation asillustrated in Fig. 3. The entire assembly of Fig. 3 is inserted in theMu metal shield 4| of Fig. 2. The coil forms 59 are also held in placeand all parts 01' the assembly of Fig. 3 are held together, bythe-shield 4|.

For holding the shield 4| within the frame 36 a sub-bridge 62 coveringthe frame or housing 36 is provided which is secured thereto in anysuitable manner as by means of screws 63. An insulating ring 64 isplaced over the assembly of Fig. 3 as shown in Fig. 2, and a spring clip55, fitting between the top bridge 62 and an insulating ring 64, isprovided to hold down the insulator 64 and to hold the assembly of Fig.3 in place within the shield 4|.

As illustrated in Figs. 3 and 4 the coil forms 44 and 45 are constructedwith apertures 66 to provide space for a spindle 61 supporting the rotor31. The spindle 61 has pivots at the upper and lower ends cooperatingwith jewel bearings of conventional type and carries a balanced bentpointer'68 also of conventional type cooperating with a graduated scale(not shown). It will be understood that suitable openings are providedin the insulator 64 and the top bridge 65 to receive the rotor spindle61.

It will be observed that a. pair of terminal lugs 89 is provided formaking connections to one of the windings A and a second pair ofterminal lugs 10 is provided for making connections to the other of thewindings B. The internalconnections of the coils are conventional andare not shown.

The top bridge 62 serves also if desired as a support for a pull-oflmagnet H for deflecting the rotor 31 to an ad scale position in case ofpower; failure, as described in Patent No. 2,181,803 granted to Faus, oras described in my copending application, Serial No, 465,081, filedNovember 9, 1942, assigned to the same asslgnee as the presentapplication. In this case the top bridge is composed of non-magneticmaterial but if more complete magnetic shielding should be desired, thetop bridge 62 may be composed of permeable magnetic material and acorresponding bottom shield may be placed at the bottom of the shield4!. In that event, I would employ a different form of pull-off magnetand a different mounting arrangement for it. For example, I may mountapproximately at the position of the screw 58, a flat plate magnetmagnetized in the direction of its thickness, such as shown at 24 inFig. 9 of the application of Harold T. Faus, Serial No. 295,597, filedSeptember 19, 1939, and assigned to the same -upon the rotor '31.

7 between the vectors R to assignee as the present application. Suitablematerial for such a flat magnet is disclosed also in Patent 2,002,445granted to Arey and Fans.

It will be observed from Figs. 3 and 4 that the winding B is composed ofcoils which are quite,

narrow in comparison with the coils comprising the-winding A.Accordingly, the winding B produces a relatively narrow magnetic fieldacting The rotor 31 is composed of high-coercive-force, exceedinglylight, transversely magnetized material composed of a mixture ofsintered oxides, such as described in Patent No. 2,248,616, granted toFaus. The rotor 31 is also similar in shape to the aforesaid rotordescribed in the above patent, except that it is flattened on the side12, the sides being parallel to the line of magnetization 13 passingthrough the poles N and S of the rotor 31. Fig. 4 illustrates thepointer 68 and the rotor 31 in the position which corresponds to thecenter scale position of the instrument.

In this position the rotor 31 has its line of magnetization 13 passingthrough the coils l2 and 43 forming the winding B, thus coinciding withthe magnetic axis of the winding B. Owing to the narrowness of themagnetic field of the coil B and the additional fact that the rotor 31is flattened on the sides so that it also has a narrow magnetic field,the component of force in the direction through the coils 42 and 43 ofthe windingB acting upon the rotor 31 is greatest when the rotor 31 isin the center coil position illustrated in Fig. 4 and least when therotor 31 is in either of the end scale positions approaching 90 degreesin either direction from the position illustrated in Fig. 4. Thus, thearrangement overcomes end compression of the scale.

The advantage obtained by the narrow fleld arrangement just'described inconnection with the rotor 31 and the auxiliary winding B will be betterunderstood by first considering the action of an instrument in which themain coil A and the cross coil B act with the same eifect on the rotorand the rotor is symmetrical with respect to its axis of rotation. Underthese circumstances the force of either coil tends to vary sinusoidallywith the angular position of the rotor. Deflection is produced in suchinstrimients, however, by variation in field strength of at least one ofthe'coils. Since in the circuit of Fig. '1 the current and fieldstrengths of the winding B are held substantially constant, deflectionis procenter scale if desired. However, ordinarily a linear angulardeflection is desired.

Referring again to Fig. 9 and recalling thatas described in connectionwith Fig. 4, the instruduced by variations in strength of the fluxproduced by the winding A.

In the vector diagram of Fig. 9 the vertical vector 3 represents theflux produced by the coil B. This vector represents the component offorce acting upon the rotor 31 in a direction through the coils l2 and43 of the winding B. The current and flux in the winding A is assumed tobe varied in five successive increments as represented by the horizontalvectors A0 to As. For these six diflerent values of current in thewinding A represented in Fig. 9, there will be six different resultantflux directions represented by the resultant vectors R0, R1, R2, Fa. R4and Re. It will be seen, however, that Wngular spacing is not uniform.Consequently, a non-uniform scale is obtained although the eflect in thecoil A was assumed to be uniform. Such a compression of the end mentthere illustrated does not have a'uniform cross force acting upon therotor 31 for different angular positions thereof notwithstandingconstancy of current in thewinding B, it will be seen that with thistype of instrument the vector B no longer represents the component offorce acting in a direction through the magnetic axis of the winding B.On the contrary, when the rotor is in the center scale position thiscomponent of force, the cross force, as it may be called forconvenience, is at a maximum value B represented by the dotted vector inFig. 9, and as the rotor deflects toward the end positions of the scale,the cross force falls to a minimum value which will be assumed to beequal to the vector B.

The action for scale end positions when the flux of the coil A equalseither A0 or A5 is unchanged.-

is represented by the vector R'z. In a similar manner other values ofresultantflux R: and R4 are obtained. It will be seen that there is asubstantially linear angular variation between the successive positionsof the vectors R'o. Ri, R's, R's, B's and R's.

I have herein shown and particularly described certain embodiments of myinvention and certain methods of operation embraced therein for thepurpose of explaining its practice and showing its application, but itwill be obvious to those skilled inthe art that many modifications andvariations are possible and I aim'therefore to cover all suchmodifications and variations as fall within the scope of my inventionwhich are defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A current responsive measuring system comprising two pairs ofresistors connected in series parallel, a current ratio responsivedevice of the.

type having a pair of'coils, a current limiting protective resistor andthree input circuit terminals, one of said bridge resistors having aresistance varying in accordance with the variations in the quantity tobe measured, said bridge resistors being connected in series parallelbetween the first and second terminals of said input terminals and eachseries pair of resistors having a junction terminal, the two junctionterminals vserving as cross-arm terminals. one of said currentresponsive coils being connected between said cross-arm terminals andthe other of said current responsive coils being connected in serieswith said current-limiting resistor between the second of said inputterminals and the third input terminals, the flrst and third inputterminals bein adapted to have a current source connected thereto forenergizing a bridge circuit.

2. A temperature responsive measuring system compensated for variationsin ambient temperature comprising a current ratio responsive instrumentof the type having a pair of windings, flrst, second and'thirdterminals, a pair of bridge resistors connected in series between thefirst an second terminals, with the Junction terminal serving as across-arm terminal, a second pair of bridge resistors also connected inseries between said first and second terminals having a junctionterminal serving as a second cross-arm terminal, a current limiting andswamping resistor connected in series with one of said currentresponsive windings between said second and third terminals, and anambient temperature compensating resistor connected in shunt across saidwinding. the second winding being connected between the cross-armterminals 01 the bridge, all oi. said resistors having negligibletemperature coemcient of resistance except one of the bridge arms whichhas a resistance varying in accordance with variations in the quantityto be measured, said first and third terminals being pted to beconnected to a source of current and said current responsive windingshaving ap-- preciable positive temperature coeflicients of resistancewhereby rising ambient temperature tends to diminish the flow of currentthrough the second instrument winding connected between the cross-armterminals and to divert. current from the first winding through theshunting ambient temperature compensating resistor to compensate fordiminution of current in the firstmentioned winding, the swampingresistor tending to maintain substantially constant the total currentthrough the shunted winding and the shuntingresistor.

3. A current responsivemeasuring system compensated for variations inambienttemperature, comprising a network including a plurality ofelements, said elements includinga variable ele-' ment the resistance 01which is a variation to be measured by the system, resistors havingnegligible temperature coemcient of resistance and a pair of windingsconsisting of windings of a current ratio responsive device, saidwindings being composed of current conducting material having anappreciable temperature coeiilcient of resistance. the first of saidwindings being connected in the network and having its currentdiminished by increasing resistance with rising temperature, the secondoi the windings being condiminution of current in the first of saidwind-.

ings with rise in temperature.

4. A current responsive measuring system com-' prising input terminalsto which a source of energizing current is adapted to be connected, aresistance network and a current ratio responsive instrument adaptedthereto having a main winding, an auxiliary winding, and a rotorresponsive in angular position to the relative effects thereon at saidwindings, the network having a variable resistance element, thevariations of which con-- stitute the variations to be measured by thesystem and the main winding of the instrument being connected in thenetwork so as to be responsive to variations in the degree of balancethereof caused by such variations to be measured, said network and saidauxiliary winding being connected in series between said inputterminals, said instrument having said auxiliary winding connected as across-fieldwinding with the magnetic axis substantially perpendicular tothe magnetic axis of the main winding, and said auxiliary winding beingrelatively narrow in comparison with the main winding whereby itproduces a relatively narrow cross-field, whereby the component oicross-field perpendicular to the field of the main winding does notremain constant but varies from a maximum with the rotor in mid scaleosition to a minimum with the rotor at end scale positions, and wherebythe measuring system is provided with calibrations of its scale which issubstantially linear over an angle approximating degrees instead ofsinusoidal.

FREDERICK R. BIAS.

